"He's, I think, it's not fair to say he's enjoying himself, it's just really stressful," Wenner said Thursday on "CBS This Morning." "At a point just gets worrisome and tired. You know he's been pounded back and forth. He's more somber. The stakes are higher. I don't know how to describe it. It's tough."

Wenner described Mr. Obama's relationship with Hillary Clinton as "great."

"It was such a smart move to have her do that (Secretary of State)," Wenner said. "She represents the United States in a way that nobody else could. She almost speaks as the president. She's got the double duty of both the diplomacy part and the symbolic part of it."

In the interview, Mr. Obama said Mitt Romney won't be able to get away from the conservative positions he took in the Republican primary race. Wenner said Obama hopes to draw sharp contrast.

Wenner thinks everybody, including the Obama people are running scared. "If you're not running scared, you're crazy. If you go in with overconfidence you're going to make mistakes. You go in there like every last vote counts and I think that's the way they mean to take it."

Wenner's impression of Mr. Obama hasn't changed over the last three years. "He as an individual appears to be as capable and confident and competent and intelligent and thoughtful and committed with a vision as about anybody we've seen in recent years. Here's a man who could be a great president."

The issue with Wenner's cover story interview with the president hits newsstands Friday.